This invention relates to methods and apparatus for cooling surfaces by evaporating a liquid refrigerant.
It is well known to produce a cooling effect by the evaporation of a liquid. A recent and particularly valuable therapeutic use of this effect is to provide localized freezing of a part of a human or animal body, e.g. in order to remove a wart or other growth. In this use, a refrigerant is maintained under pressure in a can and is dispensed, via a valve and an outlet tube, through a cotton wool bud which surrounds the discharge end of the outlet tube and which is placed on or near the site to be treated. Details of that method and of apparatus for use in that method are disclosed in U.S. Pat. No. 4,865,028 (Swart), the disclosure of which is incorporated herein by reference for all purposes.
In use of the invention described in U.S. Pat. No. 4,865,028, it has been found that the rate of evaporation (and, therefore, the rate of cooling) can be dependent on the pressure between the cotton bud and the skin; in particular, if the pressure is too great, the rate of cooling is adversely affected. It has also been found that it is difficult to obtain good results when precise placement of the cotton bud is needed, e.g. for small warts; and when the treatment site is difficult to reach; and when the treatment site is large.
I have discovered that improved results can be obtained, and in particular that the foregoing problems can be mitigated, by dispensing the liquid refrigerant though a shaped member which is composed of an open celled foam. Especially good results are obtained when the shaped member is hollow, thus providing an expansion chamber and reservoir for the refrigerant; the reservoir preferably contains a permeable and absorbent material, e.g. cotton wool.
In one preferred aspect the present invention provides an assembly for dispensing a liquid refrigerant, said assembly comprising
(1) a container which
(a) includes a valve having an inlet and an outlet, and
(b) is scaled except for the valve;
(2) a liquid refrigerant which
(a) is contained under pressure within the container and
(b) has a boiling point at atmospheric pressure of less than 0xc2x0 C.;
(3) a feed tube which has
(a) a first end within the refrigerant, and
(b) a second end which communicates with the inlet of the valve;
(4) an outlet tube which has
(a) a first end which communicates with the outlet of the valve, and
(b) a discharge end; and
(5) a dispensing head which
(a) comprises a shaped member composed of an open celled foam, and
(b) is secured to the discharge end of the outlet tube so that, when the valve is open, the liquid refrigerant is dispensed through the open celled foam.
In another preferred aspect, the present invention provides an applicator for dispensing a liquid refrigerant, said applicator comprising
(1) an outlet tube which has
(a) a first end, and
(b) a discharge end; and
(2) a dispensing head which
(a) comprises a shaped member composed of an open celled foam, and
(b) is secured to the discharge end of the outlet tube so that a liquid refrigerant supplied under pressure to the first end of the outlet tube is dispensed through the open celled foam
In another preferred aspect, the present invention provides a method of cooling the skin of a living mammal, said method comprising
(1) placing adjacent to the skin a dispensing head which comprises a shaped member composed of an open celled foam, and
(2) supplying a liquid refrigerant to the dispensing cap so that the refrigerant passes through the open celled foam and evaporates adjacent to the skin.